Micro-electro-mechanical systems (MEMS) are used in an optical element of a projector, fine nozzles formed in a head portion of an ink jet printer, and various sensors such as a pressure sensor, an acceleration sensor, and a flow rate sensor. MEMS are one of technologies for downsizing and increasing the performance of a micro device having those various sensors incorporated therein.
As an example of such a microdevice, a MEMS light scanner is illustrated in FIG. 17. As illustrated in FIG. 17, as a MEMS light scanner 100 to be incorporated in, for example, a laser printer, a fiberscope, a head mounted display, and an optical switch, there is known one including a mirror 101 having a diameter of about 1 mm, and a micro drive unit 102 configured to drive the mirror 101 (ex. Arda D. Yalcinkaya et al., “Two-Axis Electromagnetic Microscanner for High Resolution Displays,” Journal of Microelectromechanical Systems, vol. 15, no. 4, pp. 786-793, 2006).
This micro drive unit 102 is a drive unit to be driven in two axes by an electromagnetic drive system, and has double gimbal structure including a frame-shaped outer movable plate 103, outer beams 104 configured to pivotally support the outer movable plate 103 to a semiconductor substrate in a rotatable manner, and inner beams 105, which have an axial direction orthogonal to that of the outer beams 104, and are configured to pivotally support the mirror 101 serving as an inner movable plate in a rotatable manner.
In this case, the micro drive unit 102 illustrated in FIG. 17 is configured such that one beam causes rotation in one axis with a Lorentz force generated by a current, which flows through a coil formed on the outer beams, and a magnetic field, which is applied from the outside. In order to enable such two-axis drive (two degrees of freedom), the outer movable plate 103 is required on the outer side of the mirror 101. Therefore, there has been a problem in that the drive unit is upsized. When the degree of freedom is intended to be further added, a movable plate and beams are required to be added on the outer side of the outer movable plate 103. Thus, in the micro drive unit using the gimbal structure, there has been a problem in that the drive unit is upsized and complicated.
In view of this, in order to solve such problems, there has been proposed a piezoelectric drive MEMS light scanner capable of performing two-axis drive with one beam (ex. Kah How Koh et al., “A 2-D MEMS scanning mirror based on dynamic mixed mode excitation of a piezoelectric PZT thin film S-shaped actuator,” OPTICAL EXPRESS, Vol. 19, No. 15, pp. 13812-13824). The drive unit used in this light scanner has such structure that one S-shaped beam configured to pivotally support the mirror is bent by a resonant frequency ωB and is twisted by a resonant frequency ωT. However, even in this drive unit, no consideration is given to the structure for further adding the degree of freedom, and this drive unit cannot achieve three-axis drive (three degrees of freedom) or more unless the structure is changed.
As an example of other micro devices, in Japanese Laid-open Patent Publication No. 2011-191589 A, there has been proposed a one-axis micro mirror having single gimbal structure including one pair of torsion bars each connected to a support beam having unimorph structure in which upper and lower piezoelectric element layers are formed on one surface at both longitudinal ends, and a mirror to be pivotally supported by the one pair of torsion bars in a rotatable and oscillatable manner.